Drilling mud



Patented Oct. 17, 1944 stares anama mm Donald C. Bond, Northbrook,IlLQassignor to The Pure Oil Company, Chicago, 111., a corporation ofOhio No Drawing. Original 10 Claims. (01. 252-85) This invention relatesto drilling wells and is primarily concerned with the production of animproved drilling mud and composition for preparation thereof for use inthe drilling of wells, especially oil and gas wells, and with the methodof drilling wells wherein such muds are used.

application November 6, 1939, Serial No. 303,024. Divided and thisapplication May 29, r1953, Serial No. 489g061 This application is adivision of my co-pending application, Serial #303,024, filed November6,. 1939, entitled Drilling mud.

Drilling operations are usually conducted in the presence of acirculation of mud, that is, water containing mineral matter such asclay in a finely divided or defiocculated state. Such drilling muds areused in almost all rotary drilling operations v for deep wells for oiland gas and simultaneously to, the formation in which the well isdrilled, al-

though it is often necessary to add additional material to the mud whichwill increase the specific gravity in order to increase the weight ofthe column of mud in the well and thereby offset the effect of high gaspressure. For this purpose weighting materials such as iron oxide andbarytes are commonly used. Every natural clay contains particles of manyorders of magnitude, some being coarse enough tosettle out of a watersuspension quickly and others being fine enough to stay suspended forindefinite periods; In a clay that is considered good for drillingpurposes the line material is predominant and is in an indefinitely finestate of subdivision, the finest being so small that much or most of itcan be said to be in the form of a colloidal suspension or-dispersionwhen the clay has been mixed with water. The suspended particles obeythe general rules of colloidal dispersionsfithe degree of dispersion,being increased by some ions and chemicals and being decreased byothers. An increase in the degree of dispersion is termed deflocculationand a decrease in the state of dispersion is termed flocculation.Flocculated clay may be in an equally finely divided state to that ofdeflocculated clay but the fiocculated material will come together infloc'culent, loose clumps or aggregates which settle readily fromthemedium in which it is dis- 'persed,.which in the case of drilling muds,is generally water. The stability of colloidal dispersions is alsodirectly related to the charges on the vdispersed particles, In generalit may be said that strongly charged negative or positive particles formstable dispersions, whereas weakly chargedor neutral particles tend tofiocculate and settle out of the disperse medium. y when drilling insome formations such as, for example, certain shale formations,considerable difliculty has been experienced due to the property of.these shale formations of swelling andsloughing when contacted withwater or ordinary drilling mud. This property of some formations tohydrate or absorb water and swell sometimes .oc-

.curs to such an extent that the holes cave and fill to such a degreethat in the .end the drilling a has to be abandoned. Formations whichhave this property of absorbing water and swelling are, in the welldrilling art, generally termed "heavingshale formations and it is'withthese types of formations that this invention is particularly concerned.i

It is an object of this inventionto provide an improved compositionuseful in the preparation of drilling mud. I

It is another object of this invention to provide an improved drillingmud which will prevent the heaving of heaving-shale formations.

It is a still further object of this invention to provide a drilling mudin which the colloidal mineral content is dispersedas positively chargedparticles. 1

A further object of this invention is to provide an improved method fordrilling in heavin shale formations. I

Various other objects and advantages will appear as the description ofthe invention proceeds.

Colloidally dispersed clay, obeying the general rules of colloidaldispersions, carries an electrical charge. Practically all naturallyoccurring finely divided clays such as kaolin and bentonite carrynegative charges on the dispersed particles when dispersed-in an aqueousmedium. It is known that the shale in heaving-shale formation isgenerally bentonitic in character and that upon being dispersed in watercarries a negative charge. It has now been found that if the colloidallydispersed particles, generally clay, in drilling muds are positivelyinstead of negatively charged, the swelling Y of heaving-shale can beprevented or lessened to a great extent.

- In the preparation of drilling mud it is generally desirable to use afinely divided solid which will have a high colloidal dispersion inwater so as to produce a viscous, relatively stable mud with a minimumamount of solids. Bentonite has the aforesaid property and has beenfound to be a particularly satisfactory clay for use in V drilling mud.Like other similar clays, benton-' ite carries anegative electricalcharge when colloidally dispersed in an aqueous medium.

It has been found that such negatively charged colloids may be changedto positive colloids by the addition of one or more suitable watersoluble chemical compounds from the group: salts of metals wherein thepositive valence is three or more, such as thorium, aluminum, cerium andlanthanum salts; acid proteins such as acid gela-.

tin or casein; basic dyes such as methylene blue, methylene green,methylene grey, methyl violet, Bismarck brown R, Rhod amineB,acrifiavine, chrysoidin Y and chrysoidin B. By the addition of one ormore of the foregoing materials,

the negatively charged colloidal clay or bentonite may be firstneutralized and flocculated and upon a further addition, the neutralizedclay maybe deflocculated and remain in a stable dispersed state aspositively charged particles. It is not desirable to use theflocculated, neutralized particles in drilling mud' since theseparticles are not stably dispersed, the particles readily settling froman aqueous dispersion medium. When such a positively charged clay as.for example, bentonite, is dispersed in water and used as drilling mud,the shale in heaving-shale formations does not swell or slough off,into'the hole and the bentonite particles remain stably dispersed. Theability of the'positively charged bentonite to prevent swelling of theshale is believed to be due to neutralization of the negative charges onthe shale particles in the subsurface formation by the positive chargeson the bentqnite in the drilling mud with resultant formation of aflocculated iilm of shale and bentonite on the exposed surface of theshale formation in the bore hole. The flocculated mater-lat forms anextremely coherent layer and v adheres'tightly to the surface of theformation. thus substantially preventing further neutralize and at thesame time substantially preventing the ingress 01." further water to theformation, thereby preventing hydration, and swelling of the heavingshale.

In order to better determine the effect of some of the preferredmaterials upon negatively charged aqueous colloidal dispersions,mixtures of several basic water soluble dyes and bentonite were testedby means of cataphoresis experiments. The Burton apparatus wasemployedin the test. This apparatus iswell known for determining theelectrical charge on colloid particles. The results'of the tests aregiven in Table I:

TABLE I Cc. of 5% dye solution Cc. 055% bentonite Kind of dye suspensionNegative.

None Metiylene blue. o

' 0. Positive.

Do. Solid. Positive.

Do. Slightly positive.

Do. Positive.

Do. Solid. None.

Positive.

Slightly positive.

None.

Positive.

Positive.

S 8 $8888 8 83895138288 888328 888 SS888888888 Slightly posltlve.Positive.

Bhodamine a..-

-...do .do

Slightly positive.

Do. Do.

None. en 1 35' m g ypos ve. Positive.

Methylene grey do Slightly positive. Positive.

' Unable to determine charge.

1 1% solution used.

In all of the examples shown in Table L 'where the volume of dyesolution plus the volume of bentonite solution was less than cc., waterwas added to bring the mixture to this volume.

From the results in Table I it will be seen that positive colloidaldispersions of bentonite may be tion of charges between the-clay of theshale. formation and the bentonite in the drilling mud readily formed byadding suitable quantities of methylene blue, chrysoidin R, methylviolet and Bismarck brown R to' negatively charged, colloidallydispersed bentonite.

Char'ge on colloid TABLE III cshales were placed in water or in drillingmud composed of the ordinary negatively charged Stability fdile-bentomte-water miIBWTeS bentonite dispersed in water, the shaleswelled weigh with TQ and disintegrated in a few hours, therebyconclusively showing that the sample was actually a Y Baritecon-Original Sp. gr. oftop a heaving-shale type material and was readilyMixture 2 3.93%; 5%? susceptible to hydration. Other samples of theshale were placed in the various dye-bentonite 6mm mixtures listed inTable I. A m 1.29 1.18

TABLE. II gg Mixture No. Charge on colloid I Effect on heaving shale I?)21%:

Disintegrates in 3 hours.

33: Mixtures A, B and C were prepared by adding B3- g Q the designatedamount of barite 57 cc. oi. a msmtegmes in less than 12 5%bentonite-water mixture to which had been added 43 cc. of a 5% solutionof Bismarck. brown a 25 dissolved in water. The remaining mixtures wereUncgangedinfidaysprepared by adding the designated amount of barite to50 cc. of a 5% bentonite-water mixture Uncgfllged in to which had beenadded 50 cc. of a 5% solution p of methyl violet dissolved in water. 153- g l From the results of Table III it will be seen Do: that thedecrease in specific gravity of such mix- Y tures after standing forthree days is negligible. Disintcgrates in less than 12 The results ofthese tests show that mixtures of 20" Positiveuue g$g v positivelycharged bentonitic drilling mudcon- Slightly positive--- c. mfi 1 tamingdye and a weighting agent may readily iii ii i t i biii fi fi fi 55? Oesanpomosa y. eeeco u 33; ing the weighted mixtures with oil well brinewas also determined. It was found that the eflect Unchanged in 5 dam 40of the brine was no more serious onthe weighted I 3gdye-bentonite mudsuspensions than on ordinary DLginte gratgsinZdgys. I drilling mudnormally used. Since viscosity is also a .very important characteristicof drilling Dc'. g s mud, experiments were carried out to determine thevarious viscosity ranges in which :weighted caused thehleaving-shale'samples to disintegrate viscosity comparative y rapidly.In those mixtures where r the collfii d was positively charged; theheaving I comPosmonofmkm r shale samples were unchanged after five daysi f I exposure, thus conclusively provlng'that posi- 4.3% Bismarck brown11, 5.1% bentonite,90%water+ v v tively charged colloidal, bentonitlcmud contaifigi-gggfggg- 555 16%B8H6M' 'g tfi wq' ing basic dye willentirely prevent the swelling 0.8%barite m1 andbvdmtmgvf heaving shalecc ""i'ie'tfitcifif'ifiifiifiifffiifzfifififfff. to

Since it is frequently necessaryto add weight- 12% Bi marck brown R,2.8% ben n w. water+ ing materials to drilling mud in order to increaser i ham, 28

Samples of shale from heaving-shale formaof the other graduate wasdetermined, a decrease tions encountered in actual drilling operationsin specific gravity in the second sample indicating. were obtained andthe hydrating or swelling that some of the weighting material hadsettled efiect of the various colloidal dispersions listed out. TableIII shows the results of these tests: in Table I, determined. Whensamples of these 5 dye-bentonite mud could be prepared. Table Iv Themixturenumbers inTable II are the same h w th r sults of theseexperiments: mixtures as shown in Table I. a

From a review of the results of Table II it will i TABLE IV be seen thatall of the mixtures tested in the 50 cataphoresis experiments thatshowed particles Viscosity of g tBismgclc carrying a, negative charge orno charge at all; er tum the specific gravity and thereby provide ameans I o t counteracting high gas pressures, it was con ii sideredadvisable to determine hether or not 35-31mm the d Tgble V Wm seen that!stable; positively charged bentonite dispersions Positivelymarged=-dye'hentomte may be of high specific gravity could be preparedsta I Prepared Possessing practically sired i 'bility tests were carriedout ifi'the following Viscosity, ater thanithat'oi waters From a n Av 50sample of positivelycharged, large number of additional qualitativetests it weighted bentonitic mud containing barytes as has o q at thedye-bentonite mi t es I the weighting agent, was poured into each ofalso p e s :l characteristics w h m y be two 100 cc. graduates. Afterfifteen minutes the varied Over a wide ne I i top 25 co. in one graduatewas weighed to deter- While various materials have been suggested m tspecifig'graviby. of th mixture. After herein as additives to drillingmud for chang three days thespeciflc gravity of the top 25 be. mgnegatively charged particles to positively charged particles, theinvention is not limited to any particular material or method foreiIecting this change but includes the use of positively chargeddrilling mud by whatever means it is obtained. Although the principlesof the invention may be applied in various ways, and the preferredmaterials used in widely varying quantitles, it is preferred to usethose water soluble materials such as salts of metals whose positivevalence is three or more, acid proteins, or basic dyes in suchquantities as will overcome the- I oi the variations in the amount ofreplaceable base in the various dispersed particles such as bentoniticclays and in the varying degree of effectiveness with which thepreferred materials impart positiv charges to colloidallydispersedparticles, it is apparent that, the relative quan--v titles used mayvary over a rather wide range. The.amount of the preferred materialrequired may be readily determined by a cataphoresis test, an amount ofadditive being used which is somewhat in excess of the amount requiredto impart a" positive. charge -to the I dispersed particles. In general,the amounts of the preferred materials which are used fall between theranges of one part of additive compound to ten parts of dry bentonite tothree parts of additive compound to one part0! dry'bentonite. While theadditive compound maybe mixed with the bentonite in the dry state andthe mixture subsequently dispersed in water as required, it is preferredto add the dye or other additive dry or dissolved in water to mud inwhichthe bentonite is already dispersed.

The term Bentonlte as used herein is used in a generic sense asincluding all'clays having highly colloidal characteristics, whetherthey are"true bentonite or not. In describing the preferred drilling mudadditives as water soluble, it is not intended to lin n't the inventionto those materials that are completely soluble in water but to includeall materials within the groups indicated which are soluble ordispersible in water to a sufficient extent to produce deflocculatedbentonitic muds having positively charged particles,

While an efiort has been made to explain the theory by which thepositively charged colloidal It is claimed:

1. In the drilling of earth bores the step of circulating through thebore during the drilling operation an aqueous mud containing positivelycharged suspended particles to which the positive charge has beenimparted by a basic dye selected from the group consisting of RhodamineB, acrifiavine, chrysoidin Y and R, methylene green and methylene greyadded in sufllcient quantity to impart a positive charge to saidparticles,

.2. In the drilling of earth bores, the step of circulating through thebore during the drilling operation, aqueous mud containing normallynegatively charged colloidally dispersed particles and sufficient basicdye selected from the group consisting of Rhodamine B, acriflavine,chrysoidin Y and R, methylene green and methylene grey. to impart apositive charge to said particles.

3. In the drilling of earth bores, the step of circulating through thebore during the drilling operation an aqueous mud containing suspendedbentonite and weighting material and sufliclent basic dye selected fromthe group consisting of Rhodamine B, acriilavine, chrysoidin Y- and R,methylene green and methylene grey to impart a positive charge to'saidparticles.

4. A drilling mud comprising an aqueous suspension of normallynegatively charged solid particles and sufiicient basic dye selectedfrom the group consisting of Rhodamine B, acriflavine, chrysoidin Y andR, methylene green and mathylene grey, to impart a positive charge tosaid particles.

5. A drilling mud comprising an aqueous suspension of bentonite andsumcient basic dye selected from the group consisting of Rhodamine B,acriflavine, chrysoidin Y and R, methylene green and methylene grey toimpart to the bentonite a positive charge.

6. A drilling mud in accordance with claim 5 containing barite. I 7. Acompositibn useful in the preparation of drilling-muds comprising amixture of. bentonite and basic dye ,selected from the group consistingof Rhodamine B, acrifiavine, chrysoidin Y and R, methylene green andmethylene grey, the basic dye being present in amount sufficient ,toimpart to the bentonite particles a positive charge when suspended inwater.

8. A composition useful in the preparation oi drilling mud comprisingcomminuted solid particles having a negative charge when suspended inwater and suflicient basic dye selected from the particles in drillingmud provide drilling mud which prevents the heaving of heaving-shaleformations, it will be understood that the invention is not to belimited'to any particular theory of operation.

group consisting of Rhodamine B, acriflavine, chrysoidin Y and R,methylene green and methylene grey to impart a positive charge to saidparticles when suspended in water.

9. Drilling mud in accordance with claim 5 in which the proportional dyeto bentonite is. 1 to 3 parts of dye to 10 to 1 parts 01' bentonite.

10. A composition in accordance with claim 7 containing 1 to 3 parts ofdye to 10 to 1 parts oi. bentonite.

DONALD c. Bonn.

